1. Field of the Invention
The present invention relates to a fringe field switching (FFS) mode liquid crystal display and a manufacturing method thereof, in which an aperture ratio is improved to decrease power consumption and internal reflection is increased to enhance outdoor readability.
2. Description of the Related Art
A fringe field switching (FFS) mode liquid crystal display (LCD) has been proposed to improve low aperture and transmittance of an in plane switching (IPS) mode LCD.
In the FFS mode LCD, a common electrode and a pixel electrode are made of a transparent conductive layer such as indium tin oxide (ITO) or the like to thereby improve its aperture ratio and transmittance as compared with the IPS mode LCD, and a fringe field is formed in a narrow interval between the common electrode and the pixel electrode to thereby further enhance the transmittance as even liquid crystal molecules above the electrodes are all controlled. For example, there are conventional FFS mode LCDs disclosed in U.S. Pat. Nos. 6,256,081 and 6,226,118, which are filed by the same present applicant.
In the meantime, the LCD is classified into a transmissive LCD using backlight and a reflective LCD using natural light. The transmissive LCD uses the backlight as a light source, so that it can display an image brightly even in dark surroundings but the backlight causes high power consumption and bad outdoor readability. On the other hand, the reflective LCD uses its surrounding natural light without the backlight, so that it can consume less power and be used in the outdoor place but it is of no use when the surroundings are dark.
In other words, the general transmissive LCD is excellent in brightness, color reproduction, contrast ration (CR), etc. as to an indoor place, but it is almost impossible to read information from the LCD because of sunlight or reflected sunlight as to the outdoor place. Due to the sunlight stronger than one hundred thousand LUX in the outdoor place, the transmissive LCD which cannot emit light by itself is deteriorated in the outdoor readability because it depends on the brightness of the backlight and the transmittance of an LCD panel. To solve this problem, it is possible to increase the brightness of the backlight, but too much power consumption is required.
Accordingly, there has been proposed a semi-transmissive LCD to solve the shortcomings of both transmissive and reflective LCDs. The semi-transmissive LCD is compatible between the reflective type and the transmissive type, so that it can consume relatively less power and be used in the dark surroundings. Such a semi-transmissive LCD has been disclosed in Korean Patent No. 666236, filed by the same present applicant.
In general, the semi-transmissive LCD has been designed to have a single cell gap structure in which a cell gap of a transmissive region is equal to that of a reflective region, or a dual cell gap structure in which the cell gap of the transmissive region is two times larger than that of the reflective region. However, when the semi-transmissive LCD is manufactured in the single cell gap structure using the same liquid crystal mode, a phase lag of the reflective region is twice that of the transmissive region, so that a voltage-reflective (V-R) curve of a reflective mode is not matched with a voltage-transmittance (V-T) curve of a transmissive mode, thereby causing inharmonious gradation and deteriorating electro-optical properties.
Accordingly, there is being manufactured a semi-transmissive LCD with the dual cell gap structure in which a transmissive region is designed to have a cell gap two times larger than that of a reflective region. In this manner, the V-R curve of the reflective mode can be matched with the V-T curve of the transmissive mode. However, if the semi-transmissive LCD is manufactured with the dual cell gap structure, stepped difference due to the cell gap between the reflective regions increases twice, so that there are difficulties in a manufacturing process, for example, non-uniform liquid crystal alignment or the like, thereby lowering productivity. Further, the semi-transmissive LCD shows a remarkably reduction in aperture ratio at the indoor place as well as its manufacturing process is complicated and difficult.
Meanwhile, the same present applicant has proposed a semi-transmissive FFS mode LCD to use both advantages of the FFS mode LCD and the semi-transmissive LCD. Such a semi-transmissive FFS mode LCD has been disclosed in Korean Patent Publication No. 2006-117465.
However, when the semi-transmissive mode is applied to the FFS mode LCD, a resin process is necessary to form a convex-concave part for increasing the reflectivity. The resin process is difficult because it cannot perfectly avoid basic contamination on the manufacturing process, and is expensive. Further, to realize the FFS mode LCD in the semi-transmissive mode, development of a compensation film, a polarization film, etc. should be preceded in association with the structure of the semi-transmissive FFS mode LCD. In other words, cost and time for development are much required.
Under the foregoing background, researches are required for employing some properties of the semi-transmissive mode LCD, such as outdoor readability or the like, while maintaining the process of manufacturing a general transmissive FFS mode LCD.